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Croteau D, Baka T, Young S, He H, Chambers JM, Qin F, Panagia M, Pimentel DR, Balschi JA, Colucci WS, Luptak I. SGLT2 inhibitor ertugliflozin decreases elevated intracellular sodium, and improves energetics and contractile function in diabetic cardiomyopathy. Biomed Pharmacother 2023; 160:114310. [PMID: 36731341 PMCID: PMC9992115 DOI: 10.1016/j.biopha.2023.114310] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 01/17/2023] [Accepted: 01/26/2023] [Indexed: 02/04/2023] Open
Abstract
BACKGROUND Elevated myocardial intracellular sodium ([Na+]i) was shown to decrease mitochondrial calcium ([Ca2+]MITO) via mitochondrial sodium/calcium exchanger (NCXMITO), resulting in decreased mitochondrial ATP synthesis. The sodium-glucose co-transporter 2 inhibitor (SGLT2i) ertugliflozin (ERTU) improved energetic deficit and contractile dysfunction in a mouse model of high fat, high sucrose (HFHS) diet-induced diabetic cardiomyopathy (DCMP). As SGLT2is were shown to lower [Na+]i in isolated cardiomyocytes, we hypothesized that energetic improvement in DCMP is at least partially mediated by a decrease in abnormally elevated myocardial [Na+]i. METHODS Forty-two eight-week-old male C57BL/6J mice were fed a control or HFHS diet for six months. In the last month, a subgroup of HFHS-fed mice was treated with ERTU. At the end of the study, left ventricular contractile function and energetics were measured simultaneously in isolated beating hearts by 31P NMR (Nuclear Magnetic Resonance) spectroscopy. A subset of untreated HFHS hearts was perfused with vehicle vs. CGP 37157, an NCXMITO inhibitor. Myocardial [Na+]i was measured by 23Na NMR spectroscopy. RESULTS HFHS hearts showed diastolic dysfunction, decreased contractile reserve, and impaired energetics as reflected by decreased phosphocreatine (PCr) and PCr/ATP ratio. Myocardial [Na+]i was elevated > 2-fold in HFHS (vs. control diet). ERTU reversed the impairments in HFHS hearts to levels similar to or better than control diet and decreased myocardial [Na+]i to control levels. CGP 37157 normalized the PCr/ATP ratio in HFHS hearts. CONCLUSIONS Elevated myocardial [Na+]i contributes to mitochondrial and contractile dysfunction in DCMP. Targeting myocardial [Na+]i and/or NCXMITO may be an effective strategy in DCMP and other forms of heart disease associated with elevated myocardial [Na+]i.
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Affiliation(s)
- Dominique Croteau
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - Tomas Baka
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - Sara Young
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - Huamei He
- Physiological NMR Core Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - Jordan M Chambers
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - Fuzhong Qin
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - Marcello Panagia
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - David R Pimentel
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - James A Balschi
- Physiological NMR Core Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - Wilson S Colucci
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA
| | - Ivan Luptak
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, USA.
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Bayley JS, Overgaard J, Pedersen TH. Quantitative model analysis of the resting membrane potential in insect skeletal muscle: Implications for low temperature tolerance. Comp Biochem Physiol A Mol Integr Physiol 2021; 257:110970. [PMID: 33932565 DOI: 10.1016/j.cbpa.2021.110970] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 04/22/2021] [Accepted: 04/26/2021] [Indexed: 01/05/2023]
Abstract
Abiotic stressors, such as cold exposure, can depolarize insect cells substantially causing cold coma and cell death. During cold exposure, insect skeletal muscle depolarization occurs through a 2-stage process. Firstly, short-term cold exposure reduces the activity of electrogenic ion pumps, which depolarize insect muscle markedly. Secondly, during long-term cold exposure, extracellular ion homeostasis is disrupted causing further depolarization. Consequently, many cold hardy insects improve membrane potential stability during cold exposure through adaptations that secure maintenance of ion homeostasis during cold exposure. Less is known about the adaptations permitting cold hardy insects to maintain membrane potential stability during the initial phase of cold exposure, before ion balance is disrupted. To address this problem it is critical to understand the membrane components (channels and transporters) that determine the membrane potential and to examine this question the present study constructed a mathematical "charge difference" model of the insect muscle membrane potential. This model was parameterized with known literature values for ion permeabilities, ion concentrations and membrane capacitance and the model was then further developed by comparing model predictions against empirical measurements following pharmacological inhibitors of the Na+/K+ ATPase, Cl- channels and symporters. Subsequently, we compared simulated and recorded membrane potentials at 0 and 31 °C and at 10-50 mM extracellular [K+] to examine if the model could describe membrane potentials during the perturbations occurring during cold exposure. Our results confirm the importance of both Na+/K+ ATPase activity and ion-selective Na+, K+ and Cl- channels, but the model also highlights that additional electroneutral flux of Na+ and K+ is needed to describe how membrane potentials respond to temperature and [K+] in insect muscle. While considerable further work is still needed, we argue that this "charge difference" model can be used to generate testable hypotheses of how insects can preserve membrane polarization in the face of stressful cold exposure.
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Affiliation(s)
- Jeppe Seamus Bayley
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
| | - Johannes Overgaard
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus C, Denmark.
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Zhang X, Hao Y. Beneficial Effects of Echinacoside on Diabetic Cardiomyopathy in Diabetic Db/Db Mice. DRUG DESIGN DEVELOPMENT AND THERAPY 2020; 14:5575-5587. [PMID: 33376302 PMCID: PMC7755380 DOI: 10.2147/dddt.s276972] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Accepted: 11/10/2020] [Indexed: 12/31/2022]
Abstract
Purpose In this study, we investigated the protective effects and mechanism of action of echinacoside (ECH) from cistanche tubulosa extract in cardiomyocytes of db/db diabetic mice. Methods Twenty healthy male db/db mice aged 8 weeks were randomly divided into db/db+ECH (n=10, ECH, 300 mg/(kg/d)), db/db (n=10, saline), and db/m control groups (n=9). Mice were monitored weekly for diet and activity. Mice were injected with 2% of pentobarbital sodium in week 10 and executed. Weight and free blood glucose (FBG) were measured weekly. Echocardiographs were used to detect cardiac function. HE staining, Sudan II staining, Masson’s trichrome staining and Tunel assays were used to evaluate myocardial tissue pathological changes, collagen fiber deposition, lipid accumulation and apoptosis rates in cardiomyocytes, respectively. Western blot and RT-PCR analysis were used to detect the expression of components of the PPAR-α/M-CPT-1 and p53/p38MAPK signaling axis. Results Compared to db/db mice, ECH groups showed lower blood glucose and lipid levels. Deterioration in cardiac function was also delayed following ECH treatment. Histopathological analysis showed that ECH significantly improved myocardial tissue in db/db mice, including reduced intercellular spaces, regular arrangements, improved extracellular matrix deposition, and reduced lipid accumulation. ECH also significantly reduced oxidative stress levels in myocardial tissue in db/db mice. Moreover, ECH inhibited PPAR-α/M-CPT-1 signaling, downregulated CD36, and upregulated glucose transporter type 4 (GLUT-4) expression in db/db mouse models of DCM. ECH also inhibited p53/p38MAPK signaling, downregulated caspase-3 and caspase-8, and upregulated Bcl-2/Bax in db/db mouse models of DCM. Conclusion ECH displays protective effects in DCM, including the inhibition of cardiac apoptosis and oxidative stress, and improved lipid metabolism in cardiomyocytes. ECH also inhibits cardiac apoptosis through its regulation of p53/p38MAPK signaling, and prevents lipid accumulation through suppression of the PPAR-α/M-CPT-1 signaling axis.
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Affiliation(s)
- Xiang Zhang
- Department of Geriatrics, Renmin Hospital of Wuhan University, Hubei, People's Republic of China
| | - Yarong Hao
- Department of Geriatrics, Renmin Hospital of Wuhan University, Hubei, People's Republic of China
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Luptak I, Qin F, Sverdlov AL, Pimentel DR, Panagia M, Croteau D, Siwik DA, Bachschmid MM, He H, Balschi JA, Colucci WS. Energetic Dysfunction Is Mediated by Mitochondrial Reactive Oxygen Species and Precedes Structural Remodeling in Metabolic Heart Disease. Antioxid Redox Signal 2019; 31:539-549. [PMID: 31088291 PMCID: PMC6648235 DOI: 10.1089/ars.2018.7707] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2019] [Revised: 04/26/2019] [Accepted: 04/29/2019] [Indexed: 12/21/2022]
Abstract
Aims: Metabolic syndrome is associated with metabolic heart disease (MHD) that is characterized by left ventricular (LV) hypertrophy, interstitial fibrosis, contractile dysfunction, and mitochondrial dysfunction. Overexpression of catalase in mitochondria (transgenic expression of catalase targeted to the mitochondria [mCAT]) prevents the structural and functional features of MHD caused by a high-fat, high-sucrose (HFHS) diet for ≥4 months. However, it is unclear whether the effect of mCAT is due to prevention of reactive oxygen species (ROS)-mediated cardiac remodeling, a direct effect on mitochondrial function, or both. To address this question, we measured myocardial function and energetics in mice, with or without mCAT, after 1 month of HFHS, before the development of cardiac structural remodeling. Results: HFHS diet for 1 month had no effect on body weight, heart weight, LV structure, myocyte size, or interstitial fibrosis. Isolated cardiac mitochondria from HFHS-fed mice produced 2.2- to 3.8-fold more H2O2, and 16%-29% less adenosine triphosphate (ATP). In isolated beating hearts from HFHS-fed mice, [phosphocreatine (PCr)] and the free energy available for ATP hydrolysis (ΔG∼ATP) were decreased, and they failed to increase with work demands. Overexpression of mCAT normalized ROS and ATP production in isolated mitochondria, and it corrected myocardial [PCr] and ΔG∼ATP in the beating heart. Innovation: This is the first demonstration that in MHD, mitochondrial ROS mediate energetic dysfunction that is sufficient to impair contractile function. Conclusion: ROS produced and acting in the mitochondria impair myocardial energetics, leading to slowed relaxation and decreased contractile reserve. These effects precede structural remodeling and are corrected by mCAT, indicating that ROS-mediated energetic impairment, per se, is sufficient to cause contractile dysfunction in MHD.
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Affiliation(s)
- Ivan Luptak
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Fuzhong Qin
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Aaron L. Sverdlov
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
- School of Medicine and Public Health, University of Newcastle, Callaghan, Australia
| | - David R. Pimentel
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Marcello Panagia
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Dominique Croteau
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Deborah A. Siwik
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Markus M. Bachschmid
- Vascular Biology Unit, Boston University School of Medicine, Boston, Massachusetts
| | - Huamei He
- Physiological NMR Core Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts
| | - James A. Balschi
- Physiological NMR Core Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts
| | - Wilson S. Colucci
- Myocardial Biology Unit, Boston University School of Medicine, Boston, Massachusetts
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Cost of auditory sharpness: Model-Based estimate of energy use by auditory brainstem "octopus" neurons. J Theor Biol 2019; 469:137-147. [PMID: 30831173 DOI: 10.1016/j.jtbi.2019.01.043] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Revised: 01/07/2019] [Accepted: 01/21/2019] [Indexed: 11/21/2022]
Abstract
Octopus cells (OCs) of the mammalian auditory brainstem precisely encode timing of fast transient sounds and tone onsets. Sharp temporal fidelity of OCs relies on low resting membrane resistance, which suggests high energy expenditure on maintaining ion gradients across plasma membrane. We provide a model-based estimate of energy consumption in resting and spiking OCs. Our results predict that a resting OC consumes up to 2.6 × 109 ATP molecules (ATPs) per second which remarkably exceeds energy consumption of other CNS neurons. Glucose usage by all OCs in the rat is nevertheless low due to their low number. Major part of the OCs energy use results from the ion mechanisms providing for the low membrane resistance: hyperpolarization-activated mixed cation conductance and low-voltage activated K+-conductance. Spatially ordered synapses-a feature of the OCs allowing them to compensate for asynchrony of the synaptic input-brings only a 12% energy saving to OCs excitability cost. Only 13% of total OC energy used for an AP generation (1.5 × 107 ATPs) is associated with the AP generation in the axon initial segment, 64%-with synaptic currents processing and 23%-with keeping resting potential.
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Luptak I, Sverdlov AL, Panagia M, Qin F, Pimentel DR, Croteau D, Siwik DA, Ingwall JS, Bachschmid MM, Balschi JA, Colucci WS. Decreased ATP production and myocardial contractile reserve in metabolic heart disease. J Mol Cell Cardiol 2018; 116:106-114. [PMID: 29409987 PMCID: PMC5871926 DOI: 10.1016/j.yjmcc.2018.01.017] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Revised: 01/25/2018] [Accepted: 01/30/2018] [Indexed: 01/08/2023]
Abstract
Metabolic syndrome is a cluster of obesity-related metabolic abnormalities that lead to metabolic heart disease (MHD) with left ventricular pump dysfunction. Although MHD is thought to be associated with myocardial energetic deficiency, two key questions have not been answered. First, it is not known whether there is a sufficient energy deficit to contribute to pump dysfunction. Second, the basis for the energy deficit is not clear. To address these questions, mice were fed a high fat, high sucrose (HFHS) 'Western' diet to recapitulate the MHD phenotype. In isolated beating hearts, we used 31P NMR spectroscopy with magnetization transfer to determine a) the concentrations of high energy phosphates ([ATP], [ADP], [PCr]), b) the free energy of ATP hydrolysis (∆G~ATP), c) the rate of ATP production and d) flux through the creatine kinase (CK) reaction. At the lowest workload, the diastolic pressure-volume relationship was shifted upward in HFHS hearts, indicative of diastolic dysfunction, whereas systolic function was preserved. At this workload, the rate of ATP synthesis was decreased in HFHS hearts, and was associated with decreases in both [PCr] and ∆G~ATP. Higher work demands unmasked the inability of HFHS hearts to increase systolic function and led to a further decrease in ∆G~ATP to a level that is not sufficient to maintain normal function of sarcoplasmic Ca2+-ATPase (SERCA). While [ATP] was preserved at all work demands in HFHS hearts, the progressive increase in [ADP] led to a decrease in ∆G~ATP with increased work demands. Surprisingly, CK flux, CK activity and total creatine were normal in HFHS hearts. These findings differ from dilated cardiomyopathy, in which the energetic deficiency is associated with decreases in CK flux, CK activity and total creatine. Thus, in HFHS-fed mice with MHD there is a distinct metabolic phenotype of the heart characterized by a decrease in ATP production that leads to a functionally-important energetic deficiency and an elevation of [ADP], with preservation of CK flux.
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Affiliation(s)
- Ivan Luptak
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - Aaron L Sverdlov
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States; Heart Failure Unit, School of Medicine and Public Health, University of Newcastle, NSW 2300, Australia
| | - Marcello Panagia
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - Fuzhong Qin
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - David R Pimentel
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - Dominique Croteau
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - Deborah A Siwik
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - Joanne S Ingwall
- Physiological NMR Core Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States
| | - Markus M Bachschmid
- Vascular Biology Unit, Boston University School of Medicine, Boston, MA, United States
| | - James A Balschi
- Physiological NMR Core Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States
| | - Wilson S Colucci
- Myocardial Biology Unit, Boston University School of Medicine, Boston, MA, United States.
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7
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Neural Energy Supply-Consumption Properties Based on Hodgkin-Huxley Model. Neural Plast 2017; 2017:6207141. [PMID: 28316842 PMCID: PMC5337805 DOI: 10.1155/2017/6207141] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Revised: 12/29/2016] [Accepted: 01/23/2017] [Indexed: 11/29/2022] Open
Abstract
Electrical activity is the foundation of the neural system. Coding theories that describe neural electrical activity by the roles of action potential timing or frequency have been thoroughly studied. However, an alternative method to study coding questions is the energy method, which is more global and economical. In this study, we clearly defined and calculated neural energy supply and consumption based on the Hodgkin-Huxley model, during firing action potentials and subthreshold activities using ion-counting and power-integral model. Furthermore, we analyzed energy properties of each ion channel and found that, under the two circumstances, power synchronization of ion channels and energy utilization ratio have significant differences. This is particularly true of the energy utilization ratio, which can rise to above 100% during subthreshold activity, revealing an overdraft property of energy use. These findings demonstrate the distinct status of the energy properties during neuronal firings and subthreshold activities. Meanwhile, after introducing a synapse energy model, this research can be generalized to energy calculation of a neural network. This is potentially important for understanding the relationship between dynamical network activities and cognitive behaviors.
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Rooney WD, Li X, Sammi MK, Bourdette DN, Neuwelt EA, Springer CS. Mapping human brain capillary water lifetime: high-resolution metabolic neuroimaging. NMR IN BIOMEDICINE 2015; 28:607-23. [PMID: 25914365 PMCID: PMC4920360 DOI: 10.1002/nbm.3294] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 01/28/2015] [Accepted: 03/02/2015] [Indexed: 05/25/2023]
Abstract
Shutter-speed analysis of dynamic-contrast-agent (CA)-enhanced normal, multiple sclerosis (MS), and glioblastoma (GBM) human brain data gives the mean capillary water molecule lifetime (τ(b)) and blood volume fraction (v(b); capillary density-volume product (ρ(†)V)) in a high-resolution (1)H2O MRI voxel (40 μL) or ROI. The equilibrium water extravasation rate constant, k(po) (τ(b)(-1)), averages 3.2 and 2.9 s(-1) in resting-state normal white matter (NWM) and gray matter (NGM), respectively (n = 6). The results (italicized) lead to three major conclusions. (A) k(po) differences are dominated by capillary water permeability (P(W)(†)), not size, differences. NWM and NGM voxel k(po) and v(b) values are independent. Quantitative analyses of concomitant population-averaged k(po), v(b) variations in normal and normal-appearing MS brain ROIs confirm P(W)(†) dominance. (B) P(W)(†) is dominated (>95%) by a trans(endothelial)cellular pathway, not the P(CA)(†) paracellular route. In MS lesions and GBM tumors, P(CA)(†) increases but P(W)(†) decreases. (C) k(po) tracks steady-state ATP production/consumption flux per capillary. In normal, MS, and GBM brain, regional k(po) correlates with literature MRSI ATP (positively) and Na(+) (negatively) tissue concentrations. This suggests that the P(W)(†) pathway is metabolically active. Excellent agreement of the relative NGM/NWM k(po)v(b) product ratio with the literature (31)PMRSI-MT CMR(oxphos) ratio confirms the flux property. We have previously shown that the cellular water molecule efflux rate constant (k(io)) is proportional to plasma membrane P-type ATPase turnover, likely due to active trans-membrane water cycling. With synaptic proximities and synergistic metabolic cooperativities, polar brain endothelial, neuroglial, and neuronal cells form "gliovascular units." We hypothesize that a chain of water cycling processes transmits brain metabolic activity to k(po), letting it report neurogliovascular unit Na(+),K(+)-ATPase activity. Cerebral k(po) maps represent metabolic (functional) neuroimages. The NGM 2.9 s(-1) k(po) means an equilibrium unidirectional water efflux of ~10(15) H2O molecules s(-1) per capillary (in 1 μL tissue): consistent with the known ATP consumption rate and water co-transporting membrane symporter stoichiometries.
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Affiliation(s)
- William D. Rooney
- Advanced Imaging Research CenterOregon Health and Science UniversityPortlandORUSA
- W. M. Keck Foundation High‐Field MRI LaboratoryOregon Health and Science UniversityPortlandORUSA
- Knight Cardiovascular InstituteOregon Health and Science UniversityPortlandORUSA
- Department of NeurologyOregon Health and Science UniversityPortlandORUSA
| | - Xin Li
- Advanced Imaging Research CenterOregon Health and Science UniversityPortlandORUSA
- W. M. Keck Foundation High‐Field MRI LaboratoryOregon Health and Science UniversityPortlandORUSA
| | - Manoj K. Sammi
- Advanced Imaging Research CenterOregon Health and Science UniversityPortlandORUSA
- W. M. Keck Foundation High‐Field MRI LaboratoryOregon Health and Science UniversityPortlandORUSA
| | | | - Edward A. Neuwelt
- Blood‐Brain Barrier ProgramOregon Health and Science UniversityPortlandORUSA
| | - Charles S. Springer
- Advanced Imaging Research CenterOregon Health and Science UniversityPortlandORUSA
- W. M. Keck Foundation High‐Field MRI LaboratoryOregon Health and Science UniversityPortlandORUSA
- Knight Cardiovascular InstituteOregon Health and Science UniversityPortlandORUSA
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Knez J, Salvi E, Tikhonoff V, Stolarz-Skrzypek K, Ryabikov A, Thijs L, Braga D, Kloch-Badelek M, Malyutina S, Casiglia E, Czarnecka D, Kawecka-Jaszcz K, Cusi D, Nawrot T, Staessen JA, Kuznetsova T. Left ventricular diastolic function associated with common genetic variation in ATP12A in a general population. BMC MEDICAL GENETICS 2014; 15:121. [PMID: 25366262 PMCID: PMC4411923 DOI: 10.1186/s12881-014-0121-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 10/22/2014] [Indexed: 01/28/2023]
Abstract
Background Left ventricular (LV) function depends on the activity of transmembrane electrolyte transporters. Failing human myocardium has lower Na+/K+ ATPase expression and higher intracellular sodium concentrations. The ATP12A gene encodes a catalytic subunit of an ATPase that can function as a Na+/K+ pump. We, therefore, investigated the association between LV function and common genetic variants in ATP12A. Methods A random sample of 1166 participants (53.7% women; mean age 49.5 years, 44.8% hypertensive) was recruited in Belgium, Poland, Italy and Russia. We measured transmitral early and late diastolic velocities (E and A) by pulsed wave Doppler, and mitral annular velocities (e’ and a’) by tissue Doppler. Using principal component analysis, we summarized 7 Doppler indexes – namely, E, A, e’ and a’ velocities, and their ratios (E/A, e’/a’, and E/e’) – into a single diastolic score. We genotyped 5 tag SNPs (rs963984, rs9553395, rs10507337, rs12872010, rs2071490) in ATP12A. In our analysis we focused on rs10507337 because it is located within a transcription factor binding site. Results In the population-based analyses while adjusting for covariables and accounting for family clusters and country, rs10507337 C allele carriers had significantly higher E/A (P = 0.003), e’ (P = 5.8×10−5), e’/a’ (P = 0.003) and diastolic score (P = 0.0001) compared to TT homozygotes. Our findings were confirmed in the haplotype analysis and in the family-based analyses in 74 informative offspring. Conclusions LV diastolic function as assessed by conventional and tissue Doppler indexes including a composite diastolic score was associated with genetic variation in ATP12A. Further experimental studies are necessary to clarify the role of ATP12A in myocardial relaxation. Electronic supplementary material The online version of this article (doi:10.1186/s12881-014-0121-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Judita Knez
- KU Leuven Department of Cardiovascular Sciences, Research Unit Hypertension and Cardiovascular Epidemiology, University of Leuven, Leuven, Belgium. .,Hypertension Division, Department of Internal Medicine, University Clinical Centre Ljubljana, Ljubljana, Slovenia.
| | - Erika Salvi
- Department of Health, University of Milano and Genomics and Bioinformatics Platform, Fondazione Filarete, Milano, Italy.
| | - Valérie Tikhonoff
- Department of Medicine, University of Padova, Padova, Italy. .,MRC Unit for Lifelong Health and Ageing at University College London, London, UK.
| | - Katarzyna Stolarz-Skrzypek
- First Department of Cardiology, Interventional Electrocardiology and Hypertension, Jagiellonian University Medical College, Krakow, Poland.
| | - Andrew Ryabikov
- Institute of Internal and Preventive Medicine, Novosibirsk, Russian Federation. .,Novosibirsk State Medical University, Novosibirsk, Russian Federation.
| | - Lutgarde Thijs
- KU Leuven Department of Cardiovascular Sciences, Research Unit Hypertension and Cardiovascular Epidemiology, University of Leuven, Leuven, Belgium.
| | - Daniele Braga
- Department of Health, University of Milano and Genomics and Bioinformatics Platform, Fondazione Filarete, Milano, Italy.
| | - Malgorzata Kloch-Badelek
- First Department of Cardiology, Interventional Electrocardiology and Hypertension, Jagiellonian University Medical College, Krakow, Poland.
| | - Sofia Malyutina
- Institute of Internal and Preventive Medicine, Novosibirsk, Russian Federation. .,Novosibirsk State Medical University, Novosibirsk, Russian Federation.
| | | | - Danuta Czarnecka
- First Department of Cardiology, Interventional Electrocardiology and Hypertension, Jagiellonian University Medical College, Krakow, Poland.
| | - Kalina Kawecka-Jaszcz
- First Department of Cardiology, Interventional Electrocardiology and Hypertension, Jagiellonian University Medical College, Krakow, Poland.
| | - Daniele Cusi
- Department of Health, University of Milano and Genomics and Bioinformatics Platform, Fondazione Filarete, Milano, Italy.
| | - Tim Nawrot
- Department of Public Health, Occupational and Environmental Medicine, KU Leuven, Leuven, Belgium. .,Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium.
| | - Jan A Staessen
- KU Leuven Department of Cardiovascular Sciences, Research Unit Hypertension and Cardiovascular Epidemiology, University of Leuven, Leuven, Belgium. .,Department of Epidemiology, Maastricht University, Maastricht, Netherlands.
| | - Tatiana Kuznetsova
- KU Leuven Department of Cardiovascular Sciences, Research Unit Hypertension and Cardiovascular Epidemiology, University of Leuven, Leuven, Belgium.
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Springer CS, Li X, Tudorica LA, Oh KY, Roy N, Chui SYC, Naik AM, Holtorf ML, Afzal A, Rooney WD, Huang W. Intratumor mapping of intracellular water lifetime: metabolic images of breast cancer? NMR IN BIOMEDICINE 2014; 27:760-73. [PMID: 24798066 PMCID: PMC4174415 DOI: 10.1002/nbm.3111] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 03/11/2014] [Accepted: 03/12/2014] [Indexed: 05/10/2023]
Abstract
Shutter-speed pharmacokinetic analysis of dynamic-contrast-enhanced (DCE)-MRI data allows evaluation of equilibrium inter-compartmental water interchange kinetics. The process measured here - transcytolemmal water exchange - is characterized by the mean intracellular water molecule lifetime (τi). The τi biomarker is a true intensive property not accessible by any formulation of the tracer pharmacokinetic paradigm, which inherently assumes it is effectively zero when applied to DCE-MRI. We present population-averaged in vivo human breast whole tumor τi changes induced by therapy, along with those of other pharmacokinetic parameters. In responding patients, the DCE parameters change significantly after only one neoadjuvant chemotherapy cycle: while K(trans) (measuring mostly contrast agent (CA) extravasation) and kep (CA intravasation rate constant) decrease, τi increases. However, high-resolution, (1 mm)(2), parametric maps exhibit significant intratumor heterogeneity, which is lost by averaging. A typical 400 ms τi value means a trans-membrane water cycling flux of 10(13) H2O molecules s(-1)/cell for a 12 µm diameter cell. Analyses of intratumor variations (and therapy-induced changes) of τi in combination with concomitant changes of ve (extracellular volume fraction) indicate that the former are dominated by alterations of the equilibrium cell membrane water permeability coefficient, PW, not of cell size. These can be interpreted in light of literature results showing that τi changes are dominated by a PW (active) component that reciprocally reflects the membrane driving P-type ATPase ion pump turnover. For mammalian cells, this is the Na(+), K(+)-ATPase pump. These results promise the potential to discriminate metabolic and microenvironmental states of regions within tumors in vivo, and their changes with therapy.
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Affiliation(s)
- Charles S Springer
- Advanced Imaging Research Center, Oregon Health and Science UniversityPortland, OR, USA
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- *Correspondence to: C. S. Springer, Jr, Advanced Imaging Research Center, Oregon Health and Science University, Portland, OR, USA. E-mail:
| | - Xin Li
- Advanced Imaging Research Center, Oregon Health and Science UniversityPortland, OR, USA
| | - Luminita A Tudorica
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- Department of Diagnostic Radiology, Oregon Health and Science UniversityPortland, OR, USA
| | - Karen Y Oh
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- Department of Diagnostic Radiology, Oregon Health and Science UniversityPortland, OR, USA
| | - Nicole Roy
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- Department of Diagnostic Radiology, Oregon Health and Science UniversityPortland, OR, USA
| | - Stephen Y-C Chui
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- Department of Hematology/Oncology, Oregon Health and Science UniversityPortland, OR, USA
| | - Arpana M Naik
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- Department of Surgical Oncology, Oregon Health and Science UniversityPortland, OR, USA
| | - Megan L Holtorf
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
- Clinical Trials Office, Oregon Health and Science UniversityPortland, OR, USA
| | - Aneela Afzal
- Advanced Imaging Research Center, Oregon Health and Science UniversityPortland, OR, USA
| | - William D Rooney
- Advanced Imaging Research Center, Oregon Health and Science UniversityPortland, OR, USA
| | - Wei Huang
- Advanced Imaging Research Center, Oregon Health and Science UniversityPortland, OR, USA
- Knight Cancer Institute, Oregon Health and Science UniversityPortland, OR, USA
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Moujahid A, D'Anjou A, Graña M. Energy demands of diverse spiking cells from the neocortex, hippocampus, and thalamus. Front Comput Neurosci 2014; 8:41. [PMID: 24782749 PMCID: PMC3986563 DOI: 10.3389/fncom.2014.00041] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 03/22/2014] [Indexed: 11/14/2022] Open
Abstract
It has long been known that neurons in the brain are not physiologically homogeneous. In response to current stimulus, they can fire several distinct patterns of action potentials that are associated with different physiological classes ranging from regular-spiking cells, fast-spiking cells, intrinsically bursting cells, and low-threshold cells. In this work we show that the high degree of variability in firing characteristics of action potentials among these cells is accompanied with a significant variability in the energy demands required to restore the concentration gradients after an action potential. The values of the metabolic energy were calculated for a wide range of cell temperatures and stimulus intensities following two different approaches. The first one is based on the amount of Na+ load crossing the membrane during a single action potential, while the second one focuses on the electrochemical energy functions deduced from the dynamics of the computational neuron models. The results show that the thalamocortical relay neuron is the most energy-efficient cell consuming between 7 and 18 nJ/cm2 for each spike generated, while both the regular and fast spiking cells from somatosensory cortex and the intrinsically-bursting cell from a cat visual cortex are the least energy-efficient, and can consume up to 100 nJ/cm2 per spike. The lowest values of these energy demands were achieved at higher temperatures and high external stimuli.
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Affiliation(s)
- Abdelmalik Moujahid
- Computational Intelligence Group, Department of Computer Science and Artificial Intelligence, University of the Basque Country UPV/EHU San Sebastián, Spain
| | - Alicia D'Anjou
- Computational Intelligence Group, Department of Computer Science and Artificial Intelligence, University of the Basque Country UPV/EHU San Sebastián, Spain
| | - Manuel Graña
- Computational Intelligence Group, Department of Computer Science and Artificial Intelligence, University of the Basque Country UPV/EHU San Sebastián, Spain
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Sohn K, Wende AR, Abel ED, Moreno AP, Sachse FB, Punske BB. Absence of glucose transporter 4 diminishes electrical activity of mouse hearts during hypoxia. Exp Physiol 2012. [PMID: 23180812 DOI: 10.1113/expphysiol.2012.070235] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Insulin resistance, which characterizes type 2 diabetes, is associated with reduced translocation of glucose transporter 4 (GLUT4) to the plasma membrane following insulin stimulation, and diabetic patients with insulin resistance show a higher incidence of ischaemia, arrhythmias and sudden cardiac death. The aim of this study was to examine whether GLUT4 deficiency leads to more severe alterations in cardiac electrical activity during cardiac stress due to hypoxia. To fulfil this aim, we compared cardiac electrical activity from cardiac-selective GLUT4-ablated (G4H-/-) mouse hearts and corresponding control (CTL) littermates. A custom-made cylindrical 'cage' electrode array measured potentials (Ves) from the epicardium of isolated, perfused mouse hearts. The normalized average of the maximal downstroke of Ves ( (|d Ves/dt(min)|na), which we previously introduced as an index of electrical activity in normal, ischaemic and hypoxic hearts, was used to assess the effects of GLUT4 deficiency on electrical activity. The |d Ves/dt(min)|na of G4H −/− and CTL hearts decreased by 75 and 47%, respectively (P < 0.05), 30 min after the onset of hypoxia. Administration of insulin attenuated decreases in values of |d Ves/dt(min)|na in G4H −/− hearts as well as in CTL hearts, during hypoxia. In general, however, G4H −/− hearts showed a severe alteration of the propagation sequence and a prolonged total activation time. Results of this study demonstrate that reduced glucose availability associated with insulin resistance and a reduction in GLUT4-mediated glucose transport impairs electrical activity during hypoxia, and may contribute to cardiac vulnerability to arrhythmias in diabetic patients.
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Affiliation(s)
- Kwanghyun Sohn
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112-5000, USA.
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Lygate CA, Bohl S, ten Hove M, Faller KME, Ostrowski PJ, Zervou S, Medway DJ, Aksentijevic D, Sebag-Montefiore L, Wallis J, Clarke K, Watkins H, Schneider JE, Neubauer S. Moderate elevation of intracellular creatine by targeting the creatine transporter protects mice from acute myocardial infarction. Cardiovasc Res 2012; 96:466-75. [PMID: 22915766 PMCID: PMC3500046 DOI: 10.1093/cvr/cvs272] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Aims Increasing energy storage capacity by elevating creatine and phosphocreatine (PCr) levels to increase ATP availability is an attractive concept for protecting against ischaemia and heart failure. However, testing this hypothesis has not been possible since oral creatine supplementation is ineffectual at elevating myocardial creatine levels. We therefore used mice overexpressing creatine transporter in the heart (CrT-OE) to test for the first time whether elevated creatine is beneficial in clinically relevant disease models of heart failure and ischaemia/reperfusion (I/R) injury. Methods and results CrT-OE mice were selected for left ventricular (LV) creatine 20–100% above wild-type values and subjected to acute and chronic coronary artery ligation. Increasing myocardial creatine up to 100% was not detrimental even in ageing CrT-OE. In chronic heart failure, creatine elevation was neither beneficial nor detrimental, with no effect on survival, LV remodelling or dysfunction. However, CrT-OE hearts were protected against I/R injury in vivo in a dose-dependent manner (average 27% less myocardial necrosis) and exhibited greatly improved functional recovery following ex vivo I/R (59% of baseline vs. 29%). Mechanisms contributing to ischaemic protection in CrT-OE hearts include elevated PCr and glycogen levels and improved energy reserve. Furthermore, creatine loading in HL-1 cells did not alter antioxidant defences, but delayed mitochondrial permeability transition pore opening in response to oxidative stress, suggesting an additional mechanism to prevent reperfusion injury. Conclusion Elevation of myocardial creatine by 20–100% reduced myocardial stunning and I/R injury via pleiotropic mechanisms, suggesting CrT activation as a novel, potentially translatable target for cardiac protection from ischaemia.
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Affiliation(s)
- Craig A Lygate
- Department of Cardiovascular Medicine, University of Oxford, Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Oxford OX3 7BN, UK.
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14
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15
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O'Hara T, Virág L, Varró A, Rudy Y. Simulation of the undiseased human cardiac ventricular action potential: model formulation and experimental validation. PLoS Comput Biol 2011; 7:e1002061. [PMID: 21637795 PMCID: PMC3102752 DOI: 10.1371/journal.pcbi.1002061] [Citation(s) in RCA: 701] [Impact Index Per Article: 53.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Accepted: 04/05/2011] [Indexed: 11/19/2022] Open
Abstract
Cellular electrophysiology experiments, important for understanding cardiac arrhythmia mechanisms, are usually performed with channels expressed in non myocytes, or with non-human myocytes. Differences between cell types and species affect results. Thus, an accurate model for the undiseased human ventricular action potential (AP) which reproduces a broad range of physiological behaviors is needed. Such a model requires extensive experimental data, but essential elements have been unavailable. Here, we develop a human ventricular AP model using new undiseased human ventricular data: Ca(2+) versus voltage dependent inactivation of L-type Ca(2+) current (I(CaL)); kinetics for the transient outward, rapid delayed rectifier (I(Kr)), Na(+)/Ca(2+) exchange (I(NaCa)), and inward rectifier currents; AP recordings at all physiological cycle lengths; and rate dependence and restitution of AP duration (APD) with and without a variety of specific channel blockers. Simulated APs reproduced the experimental AP morphology, APD rate dependence, and restitution. Using undiseased human mRNA and protein data, models for different transmural cell types were developed. Experiments for rate dependence of Ca(2+) (including peak and decay) and intracellular sodium ([Na(+)](i)) in undiseased human myocytes were quantitatively reproduced by the model. Early afterdepolarizations were induced by I(Kr) block during slow pacing, and AP and Ca(2+) alternans appeared at rates >200 bpm, as observed in the nonfailing human ventricle. Ca(2+)/calmodulin-dependent protein kinase II (CaMK) modulated rate dependence of Ca(2+) cycling. I(NaCa) linked Ca(2+) alternation to AP alternans. CaMK suppression or SERCA upregulation eliminated alternans. Steady state APD rate dependence was caused primarily by changes in [Na(+)](i), via its modulation of the electrogenic Na(+)/K(+) ATPase current. At fast pacing rates, late Na(+) current and I(CaL) were also contributors. APD shortening during restitution was primarily dependent on reduced late Na(+) and I(CaL) currents due to inactivation at short diastolic intervals, with additional contribution from elevated I(Kr) due to incomplete deactivation.
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Affiliation(s)
- Thomas O'Hara
- Cardiac Bioelectricity and Arrhythmia Center, Department of Biomedical
Engineering, Washington University in St. Louis, St. Louis, Missouri, United
States of America
| | - László Virág
- Department of Pharmacology and Pharmacotherapy, University of Szeged,
Szeged, Hungary
| | - András Varró
- Department of Pharmacology and Pharmacotherapy, University of Szeged,
Szeged, Hungary
- Division of Cardiovascular Pharmacology, Hungarian Academy of Sciences,
Szeged, Hungary
| | - Yoram Rudy
- Cardiac Bioelectricity and Arrhythmia Center, Department of Biomedical
Engineering, Washington University in St. Louis, St. Louis, Missouri, United
States of America
- * E-mail:
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16
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Hoyer K, Song Y, Wang D, Phan D, Balschi J, Ingwall JS, Belardinelli L, Shryock JC. Reducing the late sodium current improves cardiac function during sodium pump inhibition by ouabain. J Pharmacol Exp Ther 2011; 337:513-23. [PMID: 21325441 DOI: 10.1124/jpet.110.176776] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Inhibition by cardiac glycosides of Na(+), K(+)-ATPase reduces sodium efflux from myocytes and may lead to Na(+) and Ca(2+) overload and detrimental effects on mechanical function, energy metabolism, and electrical activity. We hypothesized that inhibition of sodium persistent inward current (late I(Na)) would reduce ouabain's effect to cause cellular Na(+) loading and its detrimental metabolic (decrease of ATP) and functional (arrhythmias, contracture) effects. Therefore, we determined effects of ouabain on concentrations of intracellular sodium (Na(+)(i)) and high-energy phosphates using (23)Na and (31)P NMR, the amplitude of late I(Na) using the whole-cell patch-clamp technique, and contractility and electrical activity of guinea pig isolated hearts, papillary muscles, and ventricular myocytes in the absence and presence of inhibitors of late I(Na). Ouabain (1-1.3 μM) increased Na(+)(i) and late I(Na) of guinea pig isolated hearts and myocytes by 3.7- and 4.2-fold, respectively. The late I(Na) inhibitors ranolazine and tetrodotoxin significantly reduced ouabain-stimulated increases in Na(+)(i) and late I(Na). Reductions of ATP and phosphocreatine contents and increased diastolic tension in ouabain-treated hearts were also markedly attenuated by ranolazine. Furthermore, the ouabain-induced increase of late I(Na) was also attenuated by the Ca(2+)-calmodulin-dependent kinase I inhibitors KN-93 [N-[2-[[[3-(4-chlorophenyl)-2-propenyl]methylamino]methyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulphonamide] and autocamide-2 related inhibitory peptide, but not by KN-92 [2-[N-(4'-methoxybenzenesulfonyl)]amino-N-(4'-chlorophenyl)-2-propenyl-N-methylbenzylamine phosphate]. We conclude that ouabain-induced Na(+) and Ca(2+) overload is ameliorated by the inhibition of late I(Na).
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Affiliation(s)
- Kirsten Hoyer
- Department of Biology, Gilead Sciences, Inc., Palo Alto, CA 94304, USA.
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17
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Oka C, Cha CY, Noma A. Characterization of the cardiac Na+/K+ pump by development of a comprehensive and mechanistic model. J Theor Biol 2010; 265:68-77. [PMID: 20435048 DOI: 10.1016/j.jtbi.2010.04.028] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2009] [Revised: 03/06/2010] [Accepted: 04/26/2010] [Indexed: 12/01/2022]
Abstract
A large amount of experimental data on the characteristics of the cardiac Na(+)/K(+) pump have been accumulated, but it remains difficult to predict the quantitative contribution of the pump in an intact cell because most measurements have been made under non-physiological conditions. To extrapolate the experimental findings to intact cells, we have developed a comprehensive Na(+)/K(+) pump model based on the thermodynamic framework (Smith and Crampin, 2004) of the Post-Albers reaction cycle combined with access channel mechanisms. The new model explains a variety of experimental results for the Na(+)/K(+) pump current (I(NaK)), including the dependency on the concentrations of Na(+) and K(+), the membrane potential and the free energy of ATP hydrolysis. The model demonstrates that both the apparent affinity and the slope of the substrate-I(NaK) relationship measured experimentally are affected by the composition of ions in the extra- and intracellular solutions, indirectly through alteration in the probability distribution of individual enzyme intermediates. By considering the voltage dependence in the Na(+)- and K(+)-binding steps, the experimental voltage-I(NaK) relationship could be reconstructed with application of experimental ionic compositions in the model, and the view of voltage-dependent K(+) binding was supported. Re-evaluation of charge movements accompanying Na(+) and K(+) translocations gave a reasonable number for the site density of the Na(+)/K(+) pump on the membrane. The new model is relevant for simulation of cellular functions under various interventions, such as depression of energy metabolism.
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Affiliation(s)
- Chiaki Oka
- Cell/Biodynamics Simulation Project, Kyoto University, Kyoto, Japan
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18
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Karbowski J. Thermodynamic constraints on neural dimensions, firing rates, brain temperature and size. J Comput Neurosci 2009; 27:415-36. [PMID: 19415477 DOI: 10.1007/s10827-009-0153-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Revised: 04/01/2009] [Accepted: 04/08/2009] [Indexed: 11/24/2022]
Abstract
There have been suggestions that heat caused by cerebral metabolic activity may constrain mammalian brain evolution, architecture, and function. This article investigates physical limits on brain wiring and corresponding changes in brain temperature that are imposed by thermodynamics of heat balance determined mainly by Na(+)/K(+)-ATPase, cerebral blood flow, and heat conduction. It is found that even moderate firing rates cause significant intracellular Na(+) build-up, and the ATP consumption rate associated with pumping out these ions grows nonlinearly with frequency. Surprisingly, the power dissipated by the Na(+)/K(+) pump depends biphasically on frequency, which can lead to the biphasic dependence of brain temperature on frequency as well. Both the total power of sodium pumps and brain temperature diverge for very small fiber diameters, indicating that too thin fibers are not beneficial for thermal balance. For very small brains blood flow is not a sufficient cooling mechanism deep in the brain. The theoretical lower bound on fiber diameter above which brain temperature is in the operational regime is strongly frequency dependent but finite due to synaptic depression. For normal neurophysiological conditions this bound is at least an order of magnitude smaller than average values of empirical fiber diameters, suggesting that neuroanatomy of the mammalian brains operates in the thermodynamically safe regime. Analytical formulas presented can be used to estimate average firing rates in mammals, and relate their changes to changes in brain temperature, which can have important practical applications. In general, activity in larger brains is found to be slower than in smaller brains.
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Affiliation(s)
- Jan Karbowski
- Sloan-Swartz Center for Theoretical Neurobiology, Division of Biology 216-76, California Institute of Technology, Pasadena, CA 91125, USA.
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19
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Richards JG, Sardella BA, Schulte PM. Regulation of pyruvate dehydrogenase in the common killifish, Fundulus heteroclitus, during hypoxia exposure. Am J Physiol Regul Integr Comp Physiol 2008; 295:R979-90. [PMID: 18579651 DOI: 10.1152/ajpregu.00192.2008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined the metabolic responses of the hypoxia-tolerant killifish (Fundulus heteroclitus) to 15 h of severe hypoxia and recovery with emphasis on muscle substrate usage and the regulation of the mitochondrial protein pyruvate dehydrogenase (PDH), which controls carbohydrate oxidation. Hypoxia survival involved a transient activation of substrate-level phosphorylation in muscle (decreases in [creatine phospate] and increases in [lactate]) during which time mechanisms to reduce overall ATP consumption were initiated. This metabolic transition did not affect total cellular [ATP], but had an impact on cellular energy status as indicated by large decreases in [ATP]/[ADP(free)] and [ATP]/[AMP(free)] and a significant loss of phosphorylation potential and Gibbs free energy of ATP hydrolysis (DeltafG'). The activity of PDH was rapidly (within 3 h) decreased by approximately 50% upon hypoxia exposure and remained depressed relative to normoxic samples throughout. Inactivation of PDH was primarily mediated via posttranslational modification following the accumulation of acetyl-CoA and subsequent activation of pyruvate dehydrogenase kinase (PDK). Estimated changes in cytoplasmic and mitochondrial [NAD(+)]/[NADH] did not parallel one another, suggesting the mitochondrial NADH shuttles do not function during hypoxia exposure. Large increases in the expression of PDK (PDK isoform 2) were consistent with decreased PDH activity; however, these changes in mRNA were not associated with changes in total PDK-2 protein content assessed using mammalian antibodies. No other changes in the expression of other known hypoxia-responsive genes (e.g., lactate dehydrogenase-A or -B) were observed in either muscle or liver.
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Affiliation(s)
- Jeffrey G Richards
- Dept. of Zoology, The Univ. of British Columbia, 6270 Univ. Blvd., Vancouver, BC, Canada V6T 1Z4.
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20
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Lurman GJ, Bock CH, Pörtner HO. An examination of the metabolic processes underpinning critical swimming in Atlantic cod (Gadus morhua L.) using in vivo31P-NMR spectroscopy. J Exp Biol 2007; 210:3749-56. [DOI: 10.1242/jeb.008763] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
Traditionally, critical swimming speed has been defined as the speed when a fish can no longer propel itself forward, and is exhausted. To gain a better understanding of the metabolic processes at work during a Ucrit swim test, and that lead to fatigue, we developed a method using in vivo31P-NMR spectroscopy in combination with a Brett-type swim tunnel. Our data showed that a metabolic transition point is reached when the fish change from using steady state aerobic metabolism to non-steady state anaerobic metabolism, as indicated by a significant increase in inorganic phosphate levels from 0.3±0.3 to 9.5±3.4 mol g–1, and a drop in intracellular pH from 7.48±0.03 to 6.81±0.05 in muscle. This coincides with the point when the fish change gait from subcarangiform swimming to kick-and-glide bursts. As the number of kicks increased, so too did the Pi concentration, and the pHi dropped. Both changes were maximal at Ucrit. A significant drop in Gibbs free energy change of ATP hydrolysis from –55.6±1.4 to –49.8±0.7 kJ mol–1 is argued to have been involved in fatigue. This confirms earlier findings that the traditional definition of Ucrit, unlike other critical points that are typically marked by a transition from aerobic to anaerobic metabolism, is the point of complete exhaustion of both aerobic and anaerobic resources.
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Affiliation(s)
- Glenn J. Lurman
- Alfred Wegener Institut fuer Polar und Meeresforschung, Am Handelshafen 12, 27570, Bremerhaven, Germany
| | - Christian H. Bock
- Alfred Wegener Institut fuer Polar und Meeresforschung, Am Handelshafen 12, 27570, Bremerhaven, Germany
| | - Hans-O. Pörtner
- Alfred Wegener Institut fuer Polar und Meeresforschung, Am Handelshafen 12, 27570, Bremerhaven, Germany
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Pillekamp F, Halbach M, Reppel M, Rubenchyk O, Pfannkuche K, Xi JY, Bloch W, Sreeram N, Brockmeier K, Hescheler J. Neonatal Murine Heart Slices. A Robust Model to Study Ventricular Isometric Contractions. Cell Physiol Biochem 2007; 20:837-46. [DOI: 10.1159/000110443] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/20/2007] [Indexed: 11/19/2022] Open
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22
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Crotty P, Levy WB. Effects of Na+ channel inactivation kinetics on metabolic energy costs of action potentials. Neurocomputing 2007. [DOI: 10.1016/j.neucom.2006.10.063] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Abstract
Movement of ions across the cell membrane is driven by the free energy released from ATP hydrolysis. Here we will briefly review the chemistry of Na(+), K(+)-ATPase reaction; we will also review some recent results defining the relationship between the energetic driving force and Na(+) efflux by the Na(+) pump in the normal myocardium and then discuss this relationship for pathophysiologic states in the heart.
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Affiliation(s)
- Joanne S Ingwall
- NMR Laboratory for Physiological Chemistry, Division of Cardiovascular Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
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Abstract
The action potential of the unmyelinated nerve is metabolically expensive. Using the energetic cost per unit length for the biophysically modeled action potential of the squid giant axon, we analyze this cost and identify one possible optimization. The energetic cost arising from an action potential is divided into three separate components: 1) the depolarization of the rising phase; 2) the hyperpolarization of the falling phase; and 3) the largest component, the overlapping of positive and negative currents, which has no electrical effect. Using both the Hodgkin-Huxley (HH) model and an improved version of the HH model (HHSFL), we investigate the variation of these three components as a function of easily evolvable parameters, axon diameter and ion channel densities. Assuming conduction velocity is well designed for each organism, the energy component associated with the rising phase attains a minimum near the biological values of the diameter and channel densities. This optimization is explained by the membrane capacitance per unit length. The functional capacitance is the sum of the intrinsic membrane capacitance and the gating capacitance associated with the sodium channel, and this capacitance minimizes at nearly the same values of diameter and channel density. Because capacitance is temperature independent and because this result is independent of the assumed velocity, the result generalizes to unmyelinated mammalian axons. That is, channel density is arguably an evolved property that goes hand-in-hand with the evolutionary stability of the sodium channel.
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Affiliation(s)
- Patrick Crotty
- Department of Neurological Surgery, University of Virginia Health System, Charlottesville, VA 22908-0420, USA
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25
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Melzner F, Bock C, Pörtner HO. Critical temperatures in the cephalopodSepia officinalisinvestigated usingin vivo31P NMR spectroscopy. J Exp Biol 2006; 209:891-906. [PMID: 16481578 DOI: 10.1242/jeb.02054] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARYThe present study was designed to test the hypothesis of an oxygen limitation defining thermal tolerance in the European cuttlefish (Sepia officinalis). Mantle muscle organ metabolic status and pHiwere monitored using in vivo31P NMR spectroscopy, while mantle muscle performance was determined by recording mantle cavity pressure oscillations during ventilation and spontaneous exercise.Under control conditions (15°C), changes in muscle phospho-l-arginine (PLA) and inorganic phosphate (Pi)levels could be linearly related to frequently occurring, high-pressure mantle contractions with pressure amplitudes (MMPA) of >0.2 kPa. Accordingly,mainly MMPA of >2 kPa affected muscle PLA reserves, indicating that contractions with MMPA of <2 kPa only involve the thin layers of aerobic circular mantle musculature. On average, no more than 20% of muscle PLA was depleted during spontaneous exercise under control conditions.Subjecting animals to acute thermal change at an average rate of 1 deg. h–1 led to significant Pi accumulation (equivalent to PLA breakdown) and decrements in the free energy of ATP hydrolysis(dG/dζ) at both ends of the temperature window, starting at mean critical temperatures (Tc) of 7.0 and 26.8°C,respectively. Frequent groups of high-pressure mantle contractions could not(in the warm) or only partially (in the cold) be related to net PLA breakdown in mantle muscle, indicating an oxygen limitation of routine metabolism rather than exercise-related phosphagen use. We hypothesize that it is mainly the constantly working radial mantle muscles that become progressively devoid of oxygen. Estimates of very low dG/dζ values (–44 kJ mol–1) in this compartment, along with correlated stagnating ventilation pressures in the warm, support this hypothesis. In conclusion, we found evidence for an oxygen limitation of thermal tolerance in the cuttlefish Sepia officinalis, as indicated by a progressive transition of routine mantle metabolism to an anaerobic mode of energy production.
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Affiliation(s)
- Frank Melzner
- Alfred-Wegener-Institute for Marine and Polar Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
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Fraser JA, Huang CLH. A quantitative analysis of cell volume and resting potential determination and regulation in excitable cells. J Physiol 2004; 559:459-78. [PMID: 15243134 PMCID: PMC1665115 DOI: 10.1113/jphysiol.2004.065706] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2004] [Accepted: 07/02/2004] [Indexed: 12/20/2022] Open
Abstract
This paper quantifies recent experimental results through a general physical description of the mechanisms that might control two fundamental cellular parameters, resting potential (Em) and cell volume (Vc), thereby clarifying the complex relationships between them. Em was determined directly from a charge difference (CD) equation involving total intracellular ionic charge and membrane capacitance (Cm). This avoided the equilibrium condition dEm/dt = 0 required in determinations of Em by previous work based on the Goldman-Hodgkin-Katz equation and its derivatives and thus permitted precise calculation of Em even under non-equilibrium conditions. It could accurately model the influence upon Em of changes in Cm or Vc and of membrane transport processes such as the Na+-K+-ATPase and ion cotransport. Given a stable and adequate membrane Na+-K+-ATPase density (N), Vc and Em both converged to unique steady-state values even from sharply divergent initial intracellular ionic concentrations. For any constant set of transmembrane ion permeabilities, this set point of Vc was then determined by the intracellular membrane-impermeant solute content (X-i) and its mean charge valency (zX), while in contrast, the set point of Em was determined solely by zX. Independent changes in membrane Na+ (PNa) or K+ permeabilities (PK) or activation of cation-chloride cotransporters could perturb Vc and Em but subsequent reversal of such changes permitted full recovery of both Vc and Em to the original set points. Proportionate changes in PNa, PK and N, or changes in Cl- permeability (PCl) instead conserved steady-state Vc and Em but altered their rates of relaxation following any discrete perturbation. PCl additionally determined the relative effect of cotransporter activity on Vc and Em, in agreement with recent experimental results. In contrast, changes in Xi- produced by introduction of a finite permeability term to X- (PX) that did not alter zX caused sustained changes in Vc that were independent of Em and that persisted when PX returned to zero. Where such fluxes also altered the effective zX they additionally altered the steady state Em. This offers a basis for the suggested roles of amino acid fluxes in long-term volume regulatory processes in a variety of excitable tissues.
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Affiliation(s)
- James A Fraser
- Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.
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